In recent years, the computer industry has strived to introduce system links that operate in the gigahertz regime. Due to the increase in data bandwidth and decrease in voltage margin, the attenuation and distortion caused by the channel is of much more concern than in past system generations. Hence, for successful modeling and design of signal interconnects, it is critical to determine the frequency variations of the dielectric characteristics of the signal channel, especially their frequency-dependent losses. As such, the accurate knowledge of electric properties of chip packaging and printed circuit board (PCB) materials is required.
For example, in PCBs, a widely used material is what is commonly referred to as Fire Retardant (FR)-4 material, which is relatively less expensive. FR4 is a material formed by glass strands embedded in an epoxy resin binder. Counter to its low cost benefit, the material exhibits noticeable attenuation at higher frequencies, for example at frequencies greater than 1 GHz. These losses are associated with the loss tangent of the material, wherein the complex dielectric constant, εr, of the material varies by frequency and may be expressed by the following equation:εr=ε′r−jε″r, wherein                 ε′r is the relative permittivity of the material which varies as a function of frequency; and        ε″r is the loss factor of the material which varies as a function of frequency.Loss tangent, tan δ, may be defined by the following equation in terms of the relative permittivity, ε′r, and the loss factor, ε″r:tan δ=ε″r/ε′r         
Unfortunately, when modeling transmission lines embedded in FR4, data supplied by most manufacturers for this parameter is usually measured at relatively low frequencies, for example, 60 Hz or 100 MHz. On the other hand, existing measurement techniques such as coaxial or waveguide techniques are not only impractical for in-situ measurements, they are generally inadequate for capturing higher-order effects. Hence, a method for measuring the dielectric properties, such as the dielectric constant and loss tangent, of this material and other materials in the gigahertz regime is needed.